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The Gravity Probe B spacecraft is in NASA's Payload Processing Facility 1610 on North Vandenberg Air Force Base in California and preparations are on schedule for a launch on Saturday, April 17.

The first of four solar arrays has been installed and testing has been completed. The second solar array will be installed tomorrow, March 11. Solar array installation activities are targeted for completion on March 18.

Powered-on testing of the spacecraft with the reworked Experiment Control Unit (ECU) reinstalled is complete. A detailed data analysis is confirming that the ECU is performing as desired.

Installation of small ordnance inside the Forward Equipment Enclosure (FEE) has been completed. The FEE surrounds the electronics of the Science Mission Dewar, which has valves that are opened on-orbit by these pyrotechnics to equalize pressure.

The spacecraft is currently scheduled to be transported to Space Launch Complex 2 on April 1 and mated to the Boeing Delta II rocket.

At the pad, the rocket is enclosed within the gantry-like mobile service tower and was powered up yesterday for the resumption of pre-launch testing.

The Gravity Probe B mission is a relativity experiment developed by NASA's Marshall Space Flight Center, Stanford University and Lockheed Martin. The spacecraft will test two extraordinary predictions of Albert Einstein's general theory of relativity that he advanced in 1916: the geodetic effect (how space and time are warped by the presence of the Earth) and frame dragging (how Earth's rotation drags space and time around with it).

Gravity Probe B consists of four sophisticated gyroscopes that will provide an almost perfect space-time reference system. The mission will look in a precise manner for tiny changes in the direction of spin. Gravity Probe B will be launched into a 400-nautical-mile-high polar orbit for a 16-month mission.

Government oversight of launch preparations and the countdown management on launch day is the responsibility of NASA's John F. Kennedy Space Center. The launch service is provided to NASA by Boeing Launch Services.